This invention relates to high temperature pressure transducers in general and more particularly to a high temperature transducer exhibiting precise and repeatable operating characteristics over a wide temperature range and methods of making such transducers.
There is a great need for a high temperature pressure transducer for use in areas such as satellite applications, nuclear power testing, chemical processing, aircraft engine testing and flight testing and so on.
One of the most widely used transducers is the semiconductor piezoresistive transducer. These transducers are widely employed due to the high output signals available and the relatively small size of the transducers. The prior art is replete with a number of patents describing various structures and techniques for high temperature transducers. See for example, U.S. Pat. No. 3,930,823, issued on Jan. 6, 1976 to A. D. Kurtz, et al and assigned to the assignee herein.
In that patent there is described a dielectrically isolated pressure transducer which includes a silicon diaphragm having a piezoresistive sensor mounted on the diaphragm by means of a dielectric insulator. The diaphragm is secured about a nonactive peripheral area to an annular ring housing by means of a glass bond. This technique permitted high temperature operation due to the isolation provided by means of the dielectric insulator. See for example, U.S. Pat. No. 3,800,262 entitled HIGH TEMPERATURE TRANSDUCERS AND HOUSINGS INCLUDING FABRICATION METHODS issued on Mar. 26, 1974 to A. D. Kurtz et al.
Essentially, it is desirable to provide a pressure transducer capable of operating at high temperatures such as temperatures above 325 degrees F. Conventional integrated circuit pressure transducers are limited to approximately this temperature because the isolation between the diffused piezoresistive elements and the deflecting flexural structure is accomplished by means of P-N junction isolation. For operation to temperatures of 500 degrees F. and higher some form of dielectric isolation is required. There is disclosed herein a novel structure for achieving such isolation which possesses a number of advantages over pre-existing techniques. It is, of course, further desirable to produce such transducers which exhibit linear operating characteristics over such temperature ranges and in particular which exhibit a minumum amount of creep or hysteresis over the wide temperature ranges.
Furthermore, it is desirable to produce a transducer which possesses minumum temperature induced deviations from its room temperature calibration.
It is, therefore, an object of the present invention to provide an improved high temperature transducer which exhibits such accurate temperature coefficients and which further exhibits reliable linear and repeatable operation over a wide temperature range.